1. Field of the Invention
The present invention relates to a mono-block cylinder head structure of a water cooled engine, and more particularly, to a mono-block cylinder head structure of a water cooled engine wherein a mono-block cylinder head portion which constitutes a water cooled engine is provided with a reinforcing rib.
2. Description of the Related Art
In recent years, there have been adopted many mono-block cylinders for aircraft engines.
In producing the engine body, in general, as shown in FIG. 6, an engine body 43 is constituted by joining a cylinder block 40 and a cylinder head 41 with bolts through a cylinder head gasket 42. In the figure, reference numeral 44 denotes a head cover, and reference numeral 45 denotes an oil pan.
The mono-block cylinder is made by integrally molding a cylinder portion and a cylinder head of a cylinder block, which obviates the need for a plurality of bolt boss portions, corresponding bolts and cylinder gaskets for joining the cylinder block and the cylinder head which are necessary when the cylinder block and the cylinder head are separated from each other. Thus, as it is possible to make the engine body lightweight, which is why such mono-block cylinders are much adopted, especially in aircraft engines.
In the mono-block cylinder head 46 of a water cooled engine, as shown in FIG. 7, a water jacket outer wall portion 50 is provided on a cylinder head portion 47 from an upper end of a cylinder wall portion 48 to a cylinder head ceiling portion 49 with a predetermined space between the cylinder wall portion 48 and the cylinder head ceiling portion 49. A water jacket 51 is then formed with cooling liquid stored between the cylinder wall portion 48 and the cylinder head ceiling portion 49.
In such a mono-block cylinder 46, combustion load generated during combustion in a cylinder body 53 acts in concentration on a joint portion 52 between the cylinder head ceiling portion 49 and the cylinder wall portion 48.
In order to avoid this situation there may be, for example, a method for enlarging a thickness of the above cylinder head ceiling portion 49 or the cylinder wall portion 48, or for expanding a radius of curvature of the above joint portion 52.
However, when the wall thickness is set large, the cylinder head portion 47 including the joint portion 52 shows a temperature increase during combustion because the cooling effect by the cooling liquid in the water jacket 51 is decreased. Consequently, such a temperature increase may bring about a loss in material strength of the joint portion 52 and induce non-uniformity of heat distribution in the cylinder head portion 47, and reduce the strength of the cylinder head portion 47 itself.
Further, when the radius of curvature of the joint portion 52 is made larger, it is necessary to make an escape of the end portion of pistons larger to correspond to the inner shape of the joint portion 52, thereby there was a possibility to lower a combustion efficiency and lower the engine performance such as fuel consumption, etc.
In particular, when the cylinder block is cast with aluminum alloy, the temperature of the combustion chamber side wall portion in the cylinder head portion 47 becomes 200xc2x0 C. to 300xc2x0 C. during combustion. However, since the strength of aluminum rapidly declines from about 150xc2x0 C., the aforementioned condition becomes noticeable, such that some countermeasure has been desired.
In view of this, an object of the present invention is to provide a mono-block cylinder head structure of water cooled engine that makes it impossible to effectively prevent a reduction in strength of a joint portion due to a concentration of stress from a combustion load on the joint portion between a cylinder portion and a cylinder head ceiling portion without reducing the cooling efficiency by a water jacket.
Further, another object of the present invention is to provide a mono-block cylinder head structure of a water cooled engine which aims to alleviate uneven thermal stress by improving thermal uniformity in a cylinder body, while also enabling the cooling efficiency to be improved.
In order to solve the foregoing objects, in the invention, there is provided a mono-block cylinder head structure provided with a water jacket having a water jacket outer wall portion 14 covering a cylinder upper end portion 12 and a cylinder head ceiling portion 13 of a cooling-water type engine, comprising a reinforcing rib 19, which can hold a load generated by combustion in a combustion chamber 18 formed in a cylinder 21 and which can release heat generated by combustion to the water jacket 11, at a joint portion 16 between the cylinder upper end portion 12 and the cylinder head ceiling portion 13.
Accordingly, in the invention, even when a combustion load is generated by combustion in the combustion chamber 18 formed in the engine cylinder 21 and acts upon the joint portion 16 between the cylinder upper end portion 12 and the cylinder head ceiling portion 13, the reinforcing rib 19 which can hold the load generated by combustion enables the joint portion 16 to sufficiently withstand the generated stress, so that a loss in strength in the joint portion 16 can be prevented. Furthermore, as the heat generated in the combustion chamber 18 formed in the cylinder 21 can be radiated to the water jacket 11, there is no loss in cooling effect by the water jacket 11.
Consequently, in the invention, a loss in strength in the joint portion 16 between the cylinder upper end portion 12 and the cylinder head ceiling portion 13 can be effectively prevented without lowering the cooling efficiency by the water jacket 11.
According to one form of the invention, there is provided a mono-block cylinder head structure of a water cooled engine provided with a water jacket 11 having a water jacket outer wall portion 14 covering the cylinder upper end portion 12 and the cylinder head ceiling portion 13, comprising a reinforcing rib 19, which is formed so as to be continuously rising from the cylinder upper end portion 12 at the joint portion 16 between the above cylinder upper end portion 12 and the cylinder head ceiling portion 13 in the water jacket 11, for joining a space between the joint portion 16 and the water jacket outer side wall 14.
Accordingly, in this form of the invention, when stress by combustion load generated in the combustion chamber 18 of the cylinder 21 has acted on the above joint portion 16, the stress is retained by the joint portion 16 and the reinforcing rib 19. Furthermore, the stress is input to the water jacket outer wall portion 14 through the reinforcing rib 19 and is hold also by the water jacket outer wall portion 14. Accordingly, since it is possible to distribute and hold at the plural portions the stress generated by the combustion load, the stress caused by the combustion load does not concentrate on the joint portion 16.
As a result, a loss of strength in the joint portion 16 can be effectively prevented.
Also, as the reinforcing rib 19 is joined to the water jacket outer wall portion 14, it can effectively transfer the heat generated in the combustion chamber 18 to the water jacket 11 side without the heat remaining within the reinforcing rib 19, and thus can prevent the cooling efficiency of the cylinder head 15 from being reduced.
In a yet another form of the invention, the reinforcing ribs 19 are disposed radially in a plane over the entire area in the peripheral direction of the combustion chamber 18 with predetermined intervals therebetween.
Accordingly, in this form of the invention, since the reinforcing ribs 19 are disposed radially in a plane over the entire area in the peripheral direction of the combustion chamber 18 with predetermined intervals therebetween, a plurality of radially disposed ribs 19 sustain the combustion load generated at the central portion in the combustion chamber 18, and further, can transfer the stress radially to the water jacket outer wall portion 14, such that it is possible to reliably distribute and hold the generated stress at the plural portions.
In still yet another form of the invention, the reinforcing ribs 19 are formed in a continuous planar annulus ring shape over the entire area in the peripheral direction of the cylinder head ceiling portion 13 on the outside of the cylinder head ceiling portion 13, the water jacket 11 is formed in division into the inner water jacket portion 33 and the outer water jacket portion 34, and the cooling liquid for the inner water jacket portion 33 is able to circulate in the outer water jacket portion 34.
Accordingly, the inner water jacket portion 33 is positioned at a cylinder head ceiling wall central portion 35, and the outer water jacket 34 is positioned at a cylinder upper end portion 37 whose temperature is lower than that of the central portion.
As a result, the cooling liquid inside the water jacket 11 circulates in the inner water jacket portion 33 disposed at the cylinder head ceiling wall portion 35 having a high temperature to cool a cylinder head ceiling wall portion 35, and thereafter the cooling liquid which showed a temperature increase to a predetermined temperature by heat exchange circulates into the outer water jacket portion 34 and cools the cylinder upper end portion 37. In this case, as the cylinder upper end portion 37 has a relatively lower combustion temperature than does the cylinder head ceiling wall central portion 35, even when the cooling liquid temperature has risen to the predetermined temperature, the cooling action is not impaired.
As a result, it is possible to achieve sufficient cooling by supplying a cooling liquid of the lowest temperature to the cylinder upper end portion 37 which has the highest temperature and the greatest need for cooling, while supplying a cooling liquid of not so low a temperature to the cylinder upper end portion 37 which does not have as high a temperature as the cylinder head ceiling wall central portion 35. As a result, cooling efficiency of the entire cylinder head 15 can be improved.
Furthermore, as it is possible to cool the cylinder head 15 by flowing the cooling liquid used for cooling the cylinder head ceiling wall central portion 36 at the cylinder head upper end portion 36 of the water jacket 11 directly into around the cylinder head upper end portion 37, it is possible to cool the cylinder head 15 with high cooling efficiency by effectively utilizing the cooling liquid.
Moreover, as described above, it is possible to achieve sufficient cooling by supplying the cooling liquid of the lowest temperature to the cylinder head ceiling wall central portion 35 which has the highest temperature and the largest need for cooling, while supplying the cooling liquid of not so low a temperature to around the cylinder upper end portion 37 which does not have as high a temperature as the cylinder head ceiling wall central portion 35. As a result, it becomes possible to make the thermal distribution of the cylinder head 15 uniform by cooling. Therefore it is possible to aim to alleviate the thermal stress generated by combustion and more effectively prevent a loss of strength of the cylinder head 15.
In still another form of the invention, the joint portion 16 is formed with a predetermined curvature. The reinforcing rib 19 is disposed so as to extend across an extended surface 22 formed continuously on a cylinder inner wall surface 20, and a space L between a reinforcing rib inner side surface 23 and the extended surface 22 is formed equal to or longer than the width of a radius of curvature R of the joint portion 16. A space L1 between a reinforcing rib outer side surface 24 and the extended surface 22 is formed equal to or greater than one-third of a thickness L2 of the cylinder upper end portion 12.
The purport of the thickness conditions of the reinforcing rib 19 in this form of the invention is as hereinafter described.
The range in which the stress of the load generated by combustion in the combustion chamber 18 formed in the cylinder 21 is concentrated on the joint portion 16 corresponds to the range over which the radius of curvature R of the joint portion 16 covers. Accordingly, the space L between the reinforcing rib inner side surface 23 and the above extended surface 22 must be formed equal to or greater than the radius of curvature R of the joint portion.
In addition, in order to sustain the stress acting on the joint portion 16 the instant of the combustion in the cylinder 12, analysis results reveal that one-third of the wall thickness of the cylinder upper end portion 12 during non-combustion is necessary. Therefore, it is necessary for the space L1 between the reinforcing rib outer side surface 24 and the above extended surface 22 to be formed equal to or greater than one-third the thickness of the cylinder upper end portion 12.
As a result, according to this form of the invention, when the stress by the combustion load generated in the combustion chamber 18 of the cylinder 21 acts on the joint portion 16, the stress is reliably retained by the joint portion 16 and the reinforcing rib 19. Further, the stress is input to the water jacket outer wall portion 14 through the reinforcing rib 19, and is hold also by the water jacket outer wall portion 14.
Accordingly, because it is possible to distribute and hold stress generated by a combustion load, the stress by combustion load does not concentrate on the joint portion 16. As a result, the joint portion 16 can sufficiently withstand the generated stress, such that a loss in strength in the joint portion 16 can be effectively prevented.
Moreover, since the above reinforcing rib 19 is joined to the water jacket outer wall portion 14, it is possible to effectively transfer the heat generated in the combustion chamber 18 to the water jacket 11 side, thereby preventing the cooling efficiency of the cylinder head 15 from decreasing.